Drugs that alter activity in different neurotransmitter systems can also have highly selective effects on memory and related cognitive functions that model the types of memory impairment expressed in amnesia such as in alcohol amnestic disorder (AMD) and Alzheimer~s disease (AD). Drugs, such as alcohol, can induce specific deficits in the acquisiton, retention, and retrieval of information as well as dissociative effects (where what is remembered may be drug and mood state-dependent). Benzodiazepines and alcohol disrupt explicit memory functions and meta-memory processes (both of which require cognitive control and awarenss). These effects are independent of the sedative effects of benzodiazepines. In contrast, implicit memory functions, those that do not require awareness and access to previously acquired knowledge are unaltered. Cholinergic drugs disrupt memory by impairing the ability of subjects to make use of previously acquired knowledge and therefore compromise the ability of subjects to encode and elaborate to-be-remembered information. These drugs can be used as provocative drug challenges to help substantiate the diagnosis and to identify individuals at risk for the development of alcholism. Treatments that reverse the congitive impairments of these drugs may prove useful in treating the cognitive impairments. These drugs have also been used as tools for understanding the mechanisms involved in different types of memory functions.